Correction

An earlier version of this article incorrectly stated the number of passengers killed on American Airlines Flight 77 and on United Airlines Flight 93, and the overall number of victims on the four planes that were hijacked on September 11, 2001.

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PRINCETON, New Jersey (CNN) -- Relatives of passengers and crew aboard the four airliners hijacked on September 11, 2001, heard tapes Friday of calls from the doomed planes and said later that they were moved by heroic efforts on all the flights.

"I was overwhelmed by the unbelievable courage of the passengers and crews of all four of these flights," Deborah Burlingame, sister of one of the hijacked pilots.

She spoke after a confidential Justice Department briefing for the families held at a hotel.

"I sat there wistfully wishing that this country could be as united ... and as brave in fighting the terrorists as they were in the fierce few moments of September 11. I was very proud of them," said Burlingame.

Her brother Charles was pilot of American Airlines Flight 77, which crashed into the Pentagon.

Some family members talked with reporters after the briefing, but none would elaborate on the session specifically.

Because the government hopes to introduce the calls as evidence at the trial of alleged September 11 conspirator Zacarias Moussaoui, those who attended the briefing were required to sign a non-disclosure agreement that prohibits them from discussing the contents of the tapes or the briefings. They were not allowed to make recordings or take notes during the session.

"The one thing that the [Justice Department] made irrefutably clear to us was that to the extent we disclose any information, we are only aiding the terrorists," said Hamilton Peterson, whose father and stepmother were on United Flight 93.

But one relative, Alice Hoaglan -- whose son Mark Bingham called her from one of the flights -- recounted for reporters her final call from her son.

"'Mom, this is Mark Bingham. I just want to tell you that I love you. I am on a flight from Newark to San Francisco. There are three guys on board who have taken over the plane and they say they have a bomb. You believe me don't you, Mom? I'm calling you from the air phone.' And then we were disconnected," Hoaglan said, her voice breaking.

She quickly added, "That's not information I got today. That's information I got at 6:44 a.m. Pacific Daylight Time [on September 11, 2001] from the lips of Mark Bingham."

There were 246 victims on the four jets hijacked by 19 terrorists who were later found to be acting on behalf of al Qaeda, the Islamic terrorist organization led by Saudi exile Osama bin Laden.

American Airlines Flight 11, a Boston-to-Los Angeles flight with 81 passengers and 11 crew on board, struck the World Trade Center north tower.

A second American plane, Flight 77, from Washington's Dulles International Airport to Los Angeles with 58 passengers and six crew onboard, crashed into the Pentagon.

A second United plane, Flight 93, from Newark to San Francisco with 37 passengers and seven crew onboard, crashed in rural Shanksville, Pennsylvania.

Nearly 150 people attended the session Friday.

CNN learned that calls from just two people -- flight attendants Betty Ong and Amy Sweeney, both on American Airlines Flight 11 -- were played during the three-hour briefing.

Other calls were summarized verbally by Justice Department prosecutors, and nearly an hour was devoted to questions from relatives and responses from prosecutors.

Peterson described the session Friday as "a wonderful although detailed and grisly presentation" that provided family members with more information about the final moments of the flights.

Earlier reports and investigations have indicated that passengers on Flight 93, after they learned of the three prior hijackings, fought the hijackers and prevented them from reaching a target in Washington -- believed to be the U.S. Capitol.

Two years ago, families of Flight 93 passengers heard a 30-minute cockpit voice recording played in a government briefing and said then that it generally confirmed that many passengers acted heroically.

After Friday's session, Peterson said heroism was not limited to that one plane.

The briefing "shows that it was not just [Flight] 93 with respect to heroism and commitment with respect to passengers and crew. There is no question there were many heroes on the flights," he said.

Sandy Dahl, widow of the pilot of Flight 93, described the mood in the briefing room as "very hard. It was a difficult time for all of us.

"We all held each other," she said. "We all learned a lot of things we didn't know. But that will be for the Moussaoui trial. We wouldn't do anything to jeopardize that."

Another session for family members is scheduled next month in Boston, with video hookups available for families in Washington and Los Angeles.

The briefings are being conducted by federal prosecutors and FBI agents handling the case of Moussaoui, whose trial has been delayed indefinitely by a dispute over whether Moussaoui may obtain testimony from high-level al Qaeda operatives in U.S. military custody overseas. (Full story)

"Many family members who lost loved ones on one of the flights on September 11, 2001, have contacted us requesting to know what occurred in the flights before they were intentionally crashed by the hijackers," U.S. Attorney Paul McNulty wrote in an April 13 letter that invited the families to the briefing.

"Due to the extended delays in the prosecution of the Moussaoui case, we feel it is important to provide flight families with this information now, rather than wait until the case goes to trial," he wrote. "The sole purpose of this briefing is to describe for you the evidence gathered during the investigation of this case."

Burlingame said the briefing Friday "filled in more of details for us."

She said the session affected her deeply "not so much for the bare facts -- which I had steeled myself for -- but for my incredible pride at the horror of what they faced and how they went forward very, very bravely.

"Those voices will be instrumental hopefully in bringing justice to Zacarias Moussaoui," she said.

Some family members said they were passing on the opportunity to hear the tapes. Stephen Push, whose wife was killed aboard the plane that crashed into the Pentagon, said, "It's not something I need to relive."